Feasibility of Biogeochemical Sealing of Wellbore Cements: Lab and Simulation Tests

Abstract:

To ensure permanence of carbon dioxide stored in a geologic formation it is essential to maintain wellbore integrity to prevent leakage of gas to the surface or surficial aquifers. Among others, the Mt. Simon Sandstone of the Illinois Basin has been targeted by DOE partnerships for supercritical CO₂ injection. In this study, we used lab experiments to test the feasibility of microbially-mediated sealing of a leaking wellbore and then used the data to model the biofilm growth and calcite precipitation while accounting for over nine chemical reactions. Sporosarcina pasteurii was investigated for its ability to precipitate calcium carbonate to seal fractures in cement or within the Mt. Simon Sandstone formation, at variable pressure and temperature conditions. S. pasteurii cultures were studied in a rocking autoclave at temperature (ca. 40^oC) and pressure (ca. 12 MPa) consistent with the geologic formation at depth and surficial changes were characterized before and after experimental incubations using scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM). At temperatures up to 40^oC, atmospheric pressure, and in the presence of the Mt. Simon brine (1.016 M NaCl, 0.171M CaCl₂, 0.067 M MgCl₂, 0.017 M Na₂SO₄, 0.006 M NaHCO₃), S. pasteurii thrived and showed evidence of biofilm formation using SECM. These data are the first to be applied to the newly developed computational model that extends a singular and degenerate model of biofilm growth and incorporates a variational inequality to remove the singularity. This study extends our knowledge of the stability of biologically generated carbonate species, and the associated biota, in pore-space and fractures of pertinent geological strata and cement under conditions consistent with deep storage of CO₂.